In the field of outdoor power equipment, string timmers are often used to cut grass, weeds or other vegetation in areas where conventional rotary mowers or reel mowers are unable to gain access for proper cutting. The prior art is replete with various types of cutting heads for such trimmers which are equipped with plastic or metallic string-like elements rotatable with the head to cut the vegetation.
In one category of trimmer heads, the string-like cutter elements or lines are stored on one or more reels and fed off the reel to extend the line a predetermined length for cutting. When the cutting line is exhausted, a new line must be wound into proper position about the reel. Examples of such trimmer heads are disclosed in U.S. Pat. Nos. 3,708,967 Gerst et al, 3,826,068 Ballas et al, 3,859,776 Ballas et al, 4,137,694 Hopper, 4,068,377 Kimmel et al, and 4,148,141 Hoff. Other patents in this category which disclose various mechanisms for facilitating incremental feeding of the cutting line off the storage reel are: U.S. Pat. Nos. 4,007,525 Utter, 4,131,997 Utter, 4,194,287 Palmieri et al, 4,185,381 Palmieri et al, 4,195,408 Palmieri et al, 4,242,797 Palmieri et al, and 4,276,691 Palmieri et al.
The prior art of the aforementioned category has developed to what is referred to as a "bump head" trimmer in which the cutting line is automatically fed out from a storage reel when pressure is applied to the head such as by "bumping" against the ground. A bump head trimmer is disclosed in U.S. Pat. No. 4,524,515 Oberg.
In another category of trimmer heads sometimes referred to as "fixed line" trimmer heads, one or more cutting lines of discrete length are fixed at one inner portion thereof to the trimmer head so that the free end of the line will be extended by centrifugal force into cutting position upon rotation of the cutter head. In some fixed line trimmer heads, a portion of the cutter head must be disassembled in order to install a new cutting line each time the previous line becomes worn or shortened through use. Examples of such types of fixed line trimmer heads are disclosed in U.S. Pat. Nos. 2,663,137 Asbury, 3,831,278 Voglesonger, 4,043,037 Okamoto et al, 4,062,115 Lee, 4,068,376 Briar, 4,089,114 Doolittle et al, 4,229,882 Chartier, 4,270,271 Feldman et al and 4,571,831 White.
The prior art also contains fixed line trimmer heads where the cutting line may be secured in place to the head without requiring disassembly of the head. Examples of these types appear in U.S. Pat. Nos. 2,707,859 Walker, 4,054,992 Ballas et al, 4,107,841 Jacyno et al, 4,107,841 Rebhun, 4,190,954 Walto, 4,268,964 Moore, 4,362,007 Kennedy et al, and 4,513,563 Roser et al. However, in many of these types of fixed line trimmer heads, the cutting line must be specifically shaped or carefully manipulated into position in order to secure it to the trimmer head. For example, note the specifically formed enlargements in some of the cutter lines disclosed in the aforementioned patents to Kennedy U.S. Pat. No. 4,362,007, Roser et al U.S. Pat. No. 4,513,563 and Ballas et al U.S. Pat. No. 4,054,992; and the specially equipped eyelets disclosed in the aforementioned patents to Jacyno U.S. Pat. No. 4,118,865 and Rebhun U.S. Pat. No. 4,107,841. While the cutter line disclosed in Walto U.S. Pat. No. 4,190,954 need not be specifically preformed or shaped, it must be crossed under an associated cutter line and carefully manipulated under tabs in the cutter head in order to secure it in place. In the FIG. 4 embodiment of Ballas U.S. Pat. No. 4,054,992, the cutting line must be pressed laterally and upwards into elongated passages formed in the cutter head. In Moore U.S. Pat. No. 4,268,964 the cutting line must be threaded through a loop and doubled back on itself.
The prior art discussed above represents many attempts to simplify the method and structure by which the cutter line is installed and secured to the trimmer head in order that a cutting operation may proceed without prolonged interruption and bother to install a new cutting line when the previous line becomes worn and shortened through use. The present invention is directed to this and other goals as will appear below.
For the sake of completeness, the following patents are also cited because it is through that they may be considered pertinent to the present invention even though they disclose wire brush heads rather than string trimmer heads and are considered by applicant to be less pertinent than the art cited above: U.S. Pat. Nos. 181,416 Davis, 1,526,579 Albertson and 2,102,178 Gerhardt.